Use of Thermal and Pressure Shocks to Induce Triploid Hybrid Saugeyes

The effects of thermal (heat, cold) and pressure shocks were evaluated for inducing triploidy in saugeyes (female walleye Stizostedion vitreum × male sauger S. canadense ). Sterile triploid saugeyes are preferred for stocking because fertile diploid saugeyes have, through introgression, compromised the genetic integrity of parental stocks in Ohio, Illinois, Tennessee, and Oklahoma. Pressure shock was better than both heat and cold shocks for inducing triploidy, and heat shock was better than cold shock. Heat shocks of 31°C applied 5 min after gamete activation (time of initiation, TI) for durations of 15, 20, and 25 min resulted in an average triploidy rate (±SD) of 79.8 ± 1.9% and average survival to the eyed stage of 52.2 ± 3.4% (compared with 67.5% for controls). Cold shocks of 1.2 ± 0.7°C applied at a TI of 5 min for durations of 120, 150, and 180 min resulted in 30.8 ± 1% triploidy and survival to the eyed‐stage of 24.6 ± 3.2% (compared with 35.1% for controls). In small‐scale experiments, pressure shocks of 9,000 psi (lb/in 2 ; 1 psi = 6.895 kPa) applied at a TI of 4 min for a duration of 12 min resulted in 100% triploidy and survival to the eyed‐stage of 29.2 ± 8.8% (33.8% for controls). Later TIs of 4.5 and 5 min resulted in lower triploidy and survival to the eyed stage. In large‐scale experiments, pressure shocks of 9,000 psi applied at a TI between 3 min 57 s and 4 min 55 s for a duration of 12 min resulted in 100% triploidy among hatched embryos with a hatching rate of 5.6% (23.8% for controls). Both triploidy and survival to the eyed stage of pressure‐shocked embryos did not significantly correlate with the volume of eggs shocked per batch (0.2–0.55 L). Strategies for improving the survival of pressure‐shocked embryos include using a target TI of 4 min and using undiluted sauger sperm for fertilizing walleye eggs.